Printing devices such as a copier and an MFP (Multi-function Peripheral) having a color printing function are now widespread. To perform color printing using such a printing device, there is a need to calibrate the printing device so as to accurately reproduce colors contained in pages of a print job (also referred to as color calibration). A method of such a color calibration includes a step of forming an image of a color chart in which color patches are arrayed on a sheet of paper; a step of measuring colors of the color patches formed on the sheet with an inline sensor provided in the printing device; a step of obtaining an amount of change in colors in the color chart by comparing the measured color values given by the inline sensor with the corresponding reference values (a target color value set for each patch); and performing feedback continually so that the amount of change in colors falls within an appropriate range.
As an example relating to such a color calibration, Japanese Unexamined Patent Publication (JP-A) No. 2010-201819 discloses a printing device including: a conveyance unit for conveying a printing medium in a predetermined conveying direction; a printing unit that can print an image onto the printing medium during the conveyance on the basis of printing data expressing the image; a color measuring unit for measuring colors in a region extending in the conveying direction on the printing medium; an analysis unit for analyzing a change in measured color values in the region obtained by the color measurement; and an adjustment processing unit for performing a predetermined adjustment processing about the printing unit and/or the color measuring unit according to the result of the analysis.
As another example, JP-A No. 2006-201613 discloses an image forming apparatus that adjusts an image forming condition by measuring the density of a pattern for image density measurement formed on a recording material by using an optical measuring unit. The image forming apparatus includes: a formation unit for forming a test pattern in a region designated on the recording material before adjusting the image forming condition using the pattern for image density measurement; a density difference obtaining unit for obtaining a density difference between the density of the test pattern measured by the optical measuring unit and a reference density corresponding to the test pattern; a density fluctuation determination unit for determining an existence of a density fluctuation on the basis of the density difference; and a determination unit for determining whether or not to adjust the image forming condition that uses the pattern for image density measurement, according to the determination result of the density fluctuation determination unit.
A conventional color calibration technique includes a step of printing a color chart periodically (once in a certain number of sheets or once in a certain period of time), a step of comparing measured color values of colors in the color chart with the corresponding reference values, and a step of performing color calibration if an amount of change in color exceeds a certain value. However, this method has a problem of wastes of consuming resources and time.
That is, in a conventional color calibration technique, when the prescribed number of output sheets or prescribed elapsed time is reached, a printing device prints out a color chart irrespective of a necessity of color calibration. It makes problems of increase in unusable print sheets (waste or spoiled sheets), increase in the amount of consumption of consumables, increase in waiting time for printing, or the like. Further, before the prescribed number of output sheets or prescribed elapsed time is reached, the printing device does not print out a color chart irrespective of a necessity of color calibration. Accordingly, when the printing device passed into a state that the printing device needs to be calibrated during that period, the printing device makes outputs with the color reproducibility insufficiently secured. It creates a certain number of waste or spoiled sheets and re-print processing wastes additional consumables and time, which are problems. The present invention seeks to solve the problems.